Continuous aerosol concentrator

ABSTRACT

An airborne particle monitoring device comprising a housing suitably contoured to form a chamber, inlet, outlet and exhaust means connecting with said chamber. In operation, a vacuum power source is applied to the outlet and exhaust means to conduct a particle containing air stream into the chamber where it is suspended and concentrated in a stream of stagnant air. A second stream of air conducts the concentrated particles to a suitable collection device.

O Umted States Patent 1 1 1 1 3,731,464 Brumbaugh et al. 1 1 May 8, 1973[541 CONTINUOUS AEROSOL 3,438,26I 4 1969 Collins, Jr. ..73 421.5CONCENTRATOR 405,674 6 1889 Morse ...209 139 R 993,343 5 1911 Brewster..55/I89 Inventorsr Allen D- Brumbaush; Stanford 2,606,628 8/1952Hasselwander ..55/319 Mumford, both of Frederick, Md. FOREIGN PATENTS ORAPPLICATIONS [73] Ass1gnee: The United States of America as representedby the Secretary f the 804,846 1/1969 Canada ..73 432 PS ArmyWashington, 517,774 2 1940 Great Britain ..55/418 [22] Filed: Jan. 19,1971 Appl. No.2 107,765

Primary ExaminerBernard Nozick Attorney-Harry M. Saragovitz, Edward J.Kelly and Herbert Berl [57] ABSTRACT An airborne particle monitoringdevice comprising a housing suitably contoured to form a chamber, inlet,outlet and exhaust means connecting with said chamber. In operation, avacuum power source is applied to the outlet and exhaust means toconduct a particle containing air stream into the chamber where it issuspended and concentrated in a stream of stagnant air. A second streamof air conducts theconcentrated particles to a suitable collectiondevice.

1 Claim, 2 Drawing Figures Patented May 8,1973 I I 3,731,464

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ATTORNEYI CONTINUOUS AEROSOL CONCENTRATOR The invention described hereinmay be manufactured, used, and licensed by or for the Government forgovernmental purposes without the payment to us of any royalty thereon.

This invention relates to a continuous aerosol concentrator and moreparticularly to a sampler and system whereby airborne particles in alarge volume of air are effectively concentrated into a small volume ofair for subsequent analysis.

A prior art method for the collection and concentration of particulatematter involved the conduction of an airborne stream through a collectorand into a collecting medium, e.g., water. When a sufficientconcentration has been achieved, the particles are then recovered fromthe water by any suitable means, e.g., evaporation.

In the present invention, particles, which are contained in an airstream, are borne through an orifice, concentrated. and entrained instagnant air in a chamber. Outlet means connecting the chamber conductthe concentrated particles in a second air stream from the chamber to asuitable collecting device. A third stream containing substantially anabsence of particulate matter therein is exhausted from the system byseparate means. The present system eliminates the requirement for anaqueous collection and concentration medium. The particle sample from alarge volume of air is effectively concentrated into a small volume ofair for subsequent analysis by a detection instrument.

It is an object of this invention to provide and disclose an apparatusfor the continuous concentration of particulate matter.

It is a further object of this invention to provide and disclose anapparatus wherein particles are separated from one air stream anddeposited in another air stream.

It is a further object of this invention to provide and disclose asystem for the concentration of particulate matter from a large volumeof air into a smaller volume of air for collection and subsequentanalysis.

It is a further object of this invention to provide and disclose asystem wherein particles are collected and concentrated at'lo'w negativepressures.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is an elevated sectional view of the present device.

FIG. 2 is a schematic illustration of an aerosol collection system.

Referring now to the drawing, the device comprises housing 11 suitablycontoured to form chamber 13. The device, including the housing, may beconstructed of any suitable material, e.g., metal or plastic. Lucite wasutilized in the present device. Cap 15 of housing 11 includes a threadedbore (not shown) suitably contoured to be compatible with externallythreaded tubuterior ofinlet member 17 by an angle of l08 was found togive the best results in the collection and concentration of aerosolparticles. In addition, a flat surface on the bottom of inlet member 17was also found to improve collection and concentration characteristics.Inlet member 17 is threaded through cap 15 and protrudes into chamber13. The inlet tube is held in position by compressing 0" ring 21 betweenbody cap 15 and locking ring 23. Housing 11 has a threaded bore at thebottom segment thereof, suitably contoured to be compatible withexternally threaded outlet tube 25. Outlet tube 25 is recessed at an endthereof, which is located adjacent to chamber 13. This recessed portionis designated transfer cavity 27. It has been found that the insidediameter of outlet tube 25 must be equal or less than the diameter oforifice 19 if the negative pressure of output sample of S is to be keptat a minimum. It is important that the negative pressure of the sampleof S be kept at a minimum for the effective concentration of theparticles. Exhaust port 29 is positioned at the side of housing 11. Bothoutlet tube 25 and exhaust port 29 are operably connected to vacuumpower sources 31 and 33, respectively, as illustrated in FIG. 2. Thedistance between inlet orifice l9 and transfer cavity 27 is adjustable.

In the operation of the present device, vacuum sources 31 and 33 areactivated in order to conduct particle 34 entrained in air stream S intothe open end of externally threaded tubular member 17 as indicated bythe directional arrow. The air stream exits through orifice l9 and isthen deaccelerated and suspended in stagnant air in transfer cavity 27.It has been found that the optimum air velocity from orifice 19 isbetween 1 l0 cm/second and l.5 l0 cm/second. ln the chamber, air stream5, is divided into air stream S and S Air stream S which contains theconcentrated particles, exits through outlet tube 25 and the particlesare collected on any suitable collecting means, e.g., permeable membranefilter 37. Fixed displacement pump 31 driven by constant speed motor 39,is utilized to apply pressure to filter means 37. Vacuum .pumpprotective filter 41 and valve 43, and vacuum relief valve 45 arepositioned on the conduit means between filter 37 and vacuum pump 31.The exhaust air, i.e., stream 5;, is withdrawn through port 25 by theactivation of vacuum means 33 which may comprise a pump analogous topump 31. Any conventional means to collect the particles may beutilizedin lieu of a permeable filter, e.g., impact collecting means ora continuous tape.

An unobvious advantage accruing from the practice of the presentinvention is that the particles are separated from one air stream anddeposited into another air stream. By adjusting the ratio of the two airstream flow rates, the particles can be effectively concentrated into avolume of air much smaller than that in j which they were originallycontained. This is due to the present novel structural features andcombination thereof, including the formation of a cone shaped volume ofair in transfer cavity 27, for containment of the particles which havebeen concentrated for subsequent removal by an auxiliary air streamflowing out of the apex of the cone.

An additional advantage accruing from the practice of the presentinvention is that the concentrated particles may be removed from theaerosol concentrator'by the utilization of a negative pressure of lessthan 1 inch of water although the interior of the sampler is maintainedat up to inches ofwater negative pressure.

Experimentations conducted utilizing aerosolized polystyrene latexspheres showed recoveries of 80 to 90 percent for 3.0 and 1.8 micronsize spheres, 70 to 90 percent recoveries for 1.3 micron size spheresand 20 to 30 percent recoveries for 0.8 micron size spheres at acollector rate (8,) of liters per minute and a sample output rate (8:)of 0.5 liters per minute.

Illustrative, but without limitations, the present device comprises achamber of about eleven-sixteenths inch in height and five-eighths inchin width. inlet tube 17 comprises an inside diameter of fivethirty-seconds inch. Inlet orifice 19 comprises a 0.060 bore. The angleformed by the reduction of the inside walls of inlet tube 17 to producethe bore is 108. The inside diameter of exhaust port 29 is seventhirty-seconds inch. Transfer cavity 27 is formed by machining a 59recess in that segment of outlet tube 25 adjacent the chamber.

Although we have described our invention with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction, and the combination and arrangement of parts may beresorted to without departing from the spirit and scope of the presentinvention.

Having described our invention, we claim:

1. A continuous aerosol concentrator comprising a housing suitablycontoured to form a rectangular chamber, said chamber having an inletconduit member protruding therein an end segment of the inlet memberhaving an internal reduced flat bottom end, the internal reduced segmentformingan orifice utilizing an angle designed to give maximum collectionefficiency for a desired particle, an outlet member extending from thebottom of the housing to collecting means, the interior of said outletmember having a recessed segment adjacent the chamber and connectingtherewith, the inside diameter of the outlet conduit member being equalto or less than the diameter of the orifice, and having an exhaust portcommunicating with the exterior from the chamber; and vacuum powersources connected to the outlet member and the exhaust port.

1. A continuous aerosol concentrator comprising a housing suitablycontoured to form a rectangular chamber, said chamber having an inletconduit member protruding therein an end segment of the inlet memberhaving an internal reduced flat bottom end, the internal reduced segmentforming an orifice utilizing an angle designed to give maximumcollection efficiency for a desired particle, an outlet member extendingfrom the bottom of the housing to collecting means, the interior of saidoutlet member having a recessed segment adjacent the chamber andconnecting therewith, the inside diameter of the outlet conduit memberbeing equal to or less than the diameter of the orifice, and having anexhaust port communicating with the exterior from the chamber; andvacuum power sources connected to the outlet member and the exhaustport.